This invention relates generally to a process and apparatus for the separation of complex mixtures of carbonaceous materials by sequential elution with solvents. More particularly, the invention relates to a process and apparatus for the separation of molecular constituents of coal-derived material such as coal liquefaction process streams.
In processes such as the SRC-I process for the solvent refining of coal by thermal liquefaction there is a need for the separation and characterization of coal-derived oils. While many procedures have been used over the past forty years to monitor coal conversion products, no standard procedure has evolved that is widely used to separate and characterize liquefied or solvent refined coal products. The problems with the prior procedures are that they give low or high material balance, are time consuming, and/or involve frequent subjective judgments.
The state of the prior art is described in the following prior art materials:
(1) ANALYTICAL CHEMISTRY, Volume 50, No. 9, August, 1978, page 1381+, Article Entitled "Solvent Extraction of Coal-Derived Products",
(2) FUEL, Volume 58, July, 1979, pages 539-541, Article by Burke et al. Entitled "Liquid Column Fractionation; A Method of Solvent Fractionation of Coal Liquefaction and Petroleum Products."
(3) Advanced Technology Section of the Chemical Technology Division, Oak Ridge National Laboratory, Summer, 1981, Article by Denton et al. Entitled "Development of an Automated Coal Fractionation System."
(4) FUEL, Volume 56, January, 1977 pages 9-14, Article by M. Farcasiu. Entitled "Fractionation and Structural Characterization of Coal Liquids."
(5) ANALYTICAL CHEMISTRY, Volume 54, No. 3, March, 1982, pages 372-381, Articles by Boduszynski et al. Entitled "Separation of Solvent-Refined Coal Into Solvent-Derived Fractions" and "Separation of Solvent-Refined Coal Into Compound-Class Fractions."
(6) U.S. Pat. No. 4,279,755 for "Continuous Countercurrent Ion Exchange Process."
(7) FUEL, Volume 61, November, 1982, pages 1168-1170, Article by Awadalla et al. Entitled "Alternative Procedure for the Analysis of Coal-Derived Materials for Oil, Asphaltene and Pre-asphaltene Content."
The above references are illustrative of the known art for separating very complex mixtures of carbonaceous materials using a sequence of successively stronger solvents to obtain oils, asphaltenes and preasphaltenes fractions. These different prior art techniques for carrying out this sequential extraction range from the use of sonification and centrifugation, as described in Reference (1), to using a column packed with glass beads, as in References (2) and (5), or a column packed with sand in combination with active silica packing, as in Reference (3), or a column packed with silica gel, as in Reference (4). All of the prior art techniques either employ packed columns or involve a batch type of process. While Reference (6) uses a fluidized bed, it relates to the use of a column of material used as an ion exchange resin, which material interacts with the sample and would not be applicable to the process of the invention. Reference (7) is a batch type of process in which the entire sample is coated on the bed prior to the sequential solvent extraction procedure.
Various of the above-described analytical workup procedures have been used to determine the amount of distillate, oils, asphaltenes, preasphaltenes and residue in SRC-I process streams. However, these procedures are time-consuming and are not always reliable in terms of the material balances of the fraction generated around specific units, such as, for example, the Kerr-McGee Critical Solvent Deashing Unit. Hence, there is a need to minimize turnaround time and maximize reliability in these analytical workup procedures.
It has been shown that commonly used distillation procedures yield different amounts of distillate from the same sample and that, due to thermal degradation, distillation may alter the product distribution of preasphaltenes and residue. Laboratory vacuum distillation must therefore be carried out under well-defined conditions, and should only be used to generate a distillate and not a distillate bottoms for subsequent analysis, such as the determination of asphaltenes, preasphaltenes, and residue.
Various extraction techniques will generate different amounts of oils, asphaltenes, preasphaltenes, and residue. These techniques include beaker extractions, Soxhlet extraction, beaker precipitations, solvent separation/filtration and Liquid Column Fractionation (LC/F), developed by Conoco. Most of these procedures are very time-consuming and demand great operational skill.
The turnaround time (the time elapsed from the beginning of the analysis until the time when a result is generated including both the hands-on analysis time and the unattended analysis time) for these procedures is a very important factor in process monitoring and in cost. For example, the fastest appears to be the LC/F procedure which may provide a turnaround time of the order of about nine hours for an unknown sample type. The Soxhlet and beaker extractions in combination with the beaker precipitation method for the oils/asphaltenes separation may require about five manhours of analysis time; however, the turn-around time is of the order of about two days. The sequential solvent extraction method may take about twelve manhours and the turnaround time is also about two days.
In addition to analysis time, another criterion for a reliable product workup procedure is the material balance of the weight percents from the fractions generated. If two different samples are analyzed for fraction composition, and an equal mixture (by weight) of the samples is prepared and analyzed to determine its fraction composition, the fractions obtained should match the arithmetic average of the fractions from the two initial samples. It has been shown that beaker extractions, Soxhlet extractions, beaker precipitation, and sequential solvent extraction do not generate all fractions in the same additive manner, i.e., closing the material balance.